A high-purity silicon single crystal is mainly used for the substrate of a semiconductor device. As one of the methods for producing the silicon single crystal, Czochralski process (referred to as “CZ process”) is provided. In the CZ process, as one example as shown in FIG. 8, a silicon polycrystal is filled in a quartz crucible 5 disposed in a chamber 1 of a semiconductor single crystal production device, the silicon polycrystal is heated and melted into a melt 4 by a heater 6 provided around the quartz crucible 5, then a seed crystal attached to a seed chuck 14 is immersed into the melt 4, and the seed chuck 14 is pulled up while rotating the seed chuck 14 and the quartz crucible 5 in the same direction or a reverse direction, whereby the silicon single crystal 9 is grown. In addition, in FIG. 8, a heat insulating cylinder 7 is made of a heat insulating material.
If the silicon polycrystal filled in the quartz crucible 5 is melted, SiO gas is produced and vaporized from the surface of the melt by allowing the melt 4 to react with the quartz crucible 5. If the SiO gas formed in an amorphous condition is condensed and deposited on an internal surface of the quartz crucible 5, the surface of a single crystal 9 that is being pulled up and an internal wall of the chamber 1 and the like, and the amorphous SiO is exfoliated into the melt 4, it is deposited on the single crystal that is being grown to cause dislocation and deterioration of a yield.
In addition, if the heater 6, the graphite crucible 3, or the heat insulating cylinder 7 is heated at a high temperature, CO, CO2 and the like are produced, and if the gas is mixed into the melt 4, the carbon concentration of the single crystal that is being grown is increased. In order to solve such a problem, the evaporated matters and reaction products are exhausted to the outside of a furnace by using inert gases such as argon.
Namely, as shown in arrows in FIG. 8, the inert gas introduced from above the chamber 1 goes down along the single crystal 9, then goes up along the internal wall of the quartz crucible 5 from the surface of the melt, goes down in a space between the graphite crucible 3 and the heater 6 or a space between the heater 6 and the heat insulating cylinder 7, passes through exhaust ports at a bottom of the chamber 1 and external exhaust pipes, and is finally exhausted to the outside of the furnace together with the evaporated matters and reaction products.
However, in the case of the structure as shown in FIG. 8, the evaporated matters and reaction products are deposited on the graphite crucible 3, the heater 6, the heat insulating cylinder 7 and the like while they are conveyed halfway to the outside of the furnace together with the inert gas. In the graphite crucible 3, the inert gas containing the evaporated SiO contacts with the graphite crucible to allow the SiO to react with the graphite thereby to promote a conversion of the graphite crucible 3 into SiC. Due to this phenomenon, a difference in thermal expansion coefficient between the formed SiC and graphite causes the graphite crucible 3 to be deformed as the number of use of the graphite crucible 3 is increased. On the other hand, as for the heater 6, the inert gas containing the evaporated SiO contacts with the heater 6 to allow the SiO to react with the graphite thereby to quickly thin a central section and a slit terminal section of the heater 6 that are heated at a high temperature. As a result, the temperature distribution of the melt 4 is changed to badly affect the quality of the single crystal, for example, the concentration of oxygen contained in it,
Then, in order to solve the afore-mentioned defect, in the below-mentioned Patent Reference 1, as shown in FIG. 9, an internal cylinder (heat shield) 11 is provided adjacent to an outer periphery of the heater 6 and an external cylinder (heat shield) 12 covering an internal periphery of the heat insulating cylinder 7 is provided to arrange a space between the internal cylinder 11 and the external cylinder 12 as an exhaust path, thereby to exhaust the inert gas.
According to this configuration, as shown in arrows in FIG. 9, the argon gas introduced from above the chamber 1 passes through a space between the lower end of a radiation screen 10 and the melt 4, then goes up along an internal surface of the quartz crucible 5, and goes down in a space between the internal cylinder 11 and the external cylinder 12 and is exhausted to the outside of the furnace.
Thus, because the gas such as SiO produced from the melt 4 does not contact with the graphite crucible 3 and the heater 6, the conversion of the graphite crucible 3 and the heater 6 into SiC can be delayed, whereby the useful lives of the graphite crucible 3 and the heater 6 are greatly prolonged.
In addition, the below-mentioned Patent Reference 2 describes the single crystal production device of a structure such that a heat insulating material is provided externally of the heater and the exhaust pipes are provided externally of the heat insulating material.
In addition, the below-mentioned Patent Reference 3 describes the single crystal production device of a structure such that a heat insulating material is provided externally of the heater and an exhaust pipe is provided so as to penetrate the heat insulating material.    Patent Reference 1: Japanese Patent Application Laid-Open No. H07-223894    Patent Reference 2: Japanese Patent Application Laid-Open No. H09-2892    Patent Reference 3: Japanese Patent Application Laid-Open No. 2001-10893